Stressful life events are known to be among the causes of depression. Exposure to stressful stimuli can disrupt a variety of behavioural responses which can be restored by antidepressant treatments, and this phenomenon is the basis of most animal models of depression. However, exposure to stress can also induce effects similar to treatment with antidepressant drugs. A crucial element in determining the direction of stress effects (i.e. either depressive-like or antidepressant-like effects) appears to be predictability. Experimental evidence indicates that the mesolimbic dopamine system plays a role in the ability of the CNS to respond in opposite ways to stress. The aim of this project is to compare the effects of predictable and unpredictable stress, and their interaction with treatment with antidepressants, in different behavioural responses which are relevant to depression, including two responses which are mediated by the stimulation of dopamine receptors in the mesolimbic system.